Electricity and Circuits

Question 1

In the atom, which particles can be found in the nucleus and which can be found orbiting the nucleus?

Answer 1

Protons and neutrons are in the nucleus, electrons orbit around the nucleus.

Question 2

Conventional current goes:

Answer 2

From positive to negative

Question 2

Electrons flow:

Answer 2

From negative to positive

Question 3

In this type of circuit there is just one route the current can take around the circuit. Components cannot be switched on and off separately.

Answer 3

Series circuit

Question 4

In this type of circuit there are junctions that allow the current to take different routes. Components can be switched on and off separately.

Answer 4

Parallel circuit

Question 5

What component is represented as a symbol with a X in?

Answer 5

A light bulb

Question 6

What component is represented as a symbol with an A in?

Answer 6

An ammeter

Question 7

What component is represented as a symbol with a V in?

Answer 7

a voltmeter

Question 7

Where in a circuit should an ammeter be placed?

Answer 7

in Series with the component

Question 7

Where in a circuit should a voltmeter be placed?

Answer 7

in Parallel with the component

Question 7

Current is measured in

Answer 7

Amps (A) (also called Amperes)

Question 8

Voltage (aka Potential difference) is measured in

Answer 8

Volts (V)

Question 9

What happens to the current that flows into a junction?

Answer 9

Current is conserved - current splits at a junction to travel along different branches, but the total amount entering the junction is the same as the total amount leaving.

Question 10

In a parallel circuit, the total ____________________ across each branch of the circuit is the same. When there is more than one component in each branch of a circuit the ______________________ across all the components add up to give the total supplied by the cell or battery.

Answer 10

Potential difference, or voltage, in Volts.

Question 11

What is the equation that links Charge, Current, and time

Answer 11

Charge (C) = Current (A) x time (s)

Q = I x t

Question 12

What is the unit for Charge?

Answer 12

Coulombs (C)

Question 13

What electrical quantity is represented by the letter Q?

Answer 13

Charge

Question 14

What electrical quantity is represented by the letter I?

Answer 14

Current

Question 15

What is the equation that relates electric charge, potential difference and energy transferred in a circuit?

Answer 15

Energy transferred (J) = charge moved (Q) x potential difference (V)

Question 16

What is electrical resistance?

Answer 16

The opposition to the flow of electrons. It is measured in ohms (symbol is a Greek letter omega Ω)

Question 17

What is the equation that links voltage, current and resistance?

Answer 17

Voltage (V) = current (A) x resistance (Ω)

Question 18

What happens to total resistance if you combine two resistors in series?

Answer 18

The total resistance is the sum of the individual resistances

Question 19

What happens to total resistance if you combine two resistors in parallel?

Answer 19

The total resistance is always less than either of the individual resistances

Question 20

This component is non-ohmic. The resistance is very high when the current flows in the negative direction, but low when the current flows in the positive direction.

Answer 20

Diode

Question 21

This component is non-ohmic. The resistance increases as the potential difference increases. The graph is an ‘s’ shape.

Answer 21

Filament lamp/light bulb

Question 22

This component is non-ohmic. the graph is a ‘ski-slope’ shape. The resistance varies with light intensity.

Answer 22

LDR or Light-dependent resistor

Question 23

This component is non-ohmic. the graph is a ‘ski-slope’ shape. The resistance varies with light temperature.

Answer 23

Thermistor

Question 24

What do B.I.R.D and T.U.R.D stand for when referring to non-ohmic components

Answer 24

Brightness Increases Resistance Decreases (for LDRs)

Temperaure Up Resistance Down (for Thermistors)

Question 25

Why do electrical wires get hot?

Answer 25

When a current passes through a wire energy is transferred because work is done against the resistance.

Question 26

When energy is transferred due to heating, and spreads out to give the surroundings thermal energy we say it is:

Answer 26

dissipated

Question 27

Give an example where the heating effect of a current is useful:

Answer 27

Toaster, kettle, hair dryer, electric heater - anything with a heating element.

Question 28

Give an example where the heating effect of a current is not useful:

Answer 28

A Computer, Plugs & Wires - any electronic device that is not meant to get hot.

Question 29

Resistance can be reduced by:

Answer 29

Using wires made from metals with low resistance e.g. copper or aluminium.

Using a thicker wire (larger diameter).

Cooling metals so the lattice ions are not vibrating as much.

Question 30

Describe what happens to electrons as they flow through a lattice of positive ions within a wire or component.

Answer 30

As electrons flow through the lattice of vibrating ions within a wire/component they collide with the ions. The more collisions the higher the resistance. When the electrons collide with the ions, they transfer energy to them making them heat up (and vibrate more!)

Question 31

What is the equation for calculating electrical energy in terms of current, voltage and time?

Answer 31

E = I t V

Electrical energy (J) = Current (A) x voltage (V) x time (s)

Question 32

What is power and what units are used to measure it?

Answer 32

Power is the energy transferred per second, measured in Watts (W)

Question 33

What is the equation that relates power to energy used in joules?

Answer 33

P=E/t

Power (Watts) = Energy transferred (J) / time taken (s)

Question 34

How can you calculate power when you know current, potential difference and/or resistance?

Answer 34

P = I x V

Power (W) = current (A) x voltage (v)

and

P= I2 x R

Power (Watts) = Current squared (Amps squared) x Resistance (Ohms)

Question 35

What is the voltage supply and frequency of the UK domestic electricity supply (mains)?

Answer 35

230V

50Hz

Question 36

What is alternating current?

Answer 36

Current keeps alternating direction - with a frequency of 50 Hz for the UK mains supply.

Question 37

Compare a.c. and d.c. in terms of voltage.

Answer 37

in d.c. the voltage remains constant.
In a.c. the voltage also changes - increasing to a peak voltage, then decreasing to zero before increasing to a peak negative voltage (opposite direction) then back to zero. On repeat.

Question 38

What type of voltage (alternating/direct) is supplied by the mains, and what is supplied by a battery or cell?

Answer 38

Mains = alternating

Battery/cell = direct

Question 39

How does a fuse work?

Answer 39

A fuse is a tube with a thin wire inside. The current passes through the wire and the wire gets hotter. If the current exceeds a certain value the wire melts. This breaks the circuit and stops the current. They must then be replaced.

Question 40

What colour is the Earth wire and what voltage does it carry if the circuit is correctly connected?

Answer 40

Green and yellow.
It is for safety and is at 0V if the circuit is correctly connected.

Question 40

What colour is the Live wire and what voltage does it carry if the circuit is correctly connected?

Answer 40

Brown.
It connects the appliance to the mains supply. Voltage is 230V.

Question 41

What colour is the Neutral wire and what voltage does it carry if the circuit is correctly connected?

Answer 41

Blue.
It is the return path to the power station. It carries 0V.